Improvement in centrifuges



2 Sheets-Sheet 1 Filed Dec. 30, 1957 INVENTOR. HERBERT TROTTER JR.

ATTORNEY July 2, 1963 H. TROTTER, JR 3,096,282

IMPROVEMENT IN CENTRIFUGES Filed Dec. 30, 1957 2 Sheets-Sheet 2 Fig. 2

INVENTOR. HERBERT TROTTER JR.

BYILAQ/OGM ATTORNEY United States Patent 3,696,282 IMPRQVEMENT INCENTRIFUGES Herbert Trotter, Jr., Haverford, Pa., assignor to TheSharples Corporation, a corporation of Delaware Filed Dec. 30, 1957,Ser. No. 706,061 2 Claims. (Cl. 233-7) This invention pertains generallyto centrifuges of the solids-discharge type, and particularly tocentrifuges provided with mechanical means for the movement of solids ineffecting their discharge.

Typical of centrifuges of this type are those which are provided with ahelical and/or spiral screw or scroll for the movement of separatedsolids through the zone of centnifu-gation to a discharge zone thereof.Any such screw, scroll or plow mechanism, whether comprised of a singlemember, or of a plurality of members, customarily operates by way ofsliding the separated solids along the interior wall of the centrifugerotor, the general direction of movement of the solids relative to therotor wall being along straight and/ or curved lines, e.-g. with themovement of solids following a helical and/or spiral pattern. Theinterior wall of the rotor is thus subjected to wear, the rate of whichis increased with increase in abrasiveness of the solids beingseparated. Such wear of the inner wall of the rotor not only reducesrotor strength by virtue of reduction in wall thickness, but alsoincreases the clearance between the rotor wall and the screw, scroll orplow, referred to herein generally as an impeller, thereby reducing theefficiency of the cooperating elements in the discharge of separatedsolids from the rotor.

Wear of the impeller does not present a major problem from thestandpoint of repair, except for the time and expense involved, for themetal which has been worn away can readily be replaced, such as bywelding additiona1 metal thereto in bringing it back to its originalshape and dimensions. It is impracticable, however, to employ thisexpedient for replacing metal removed by wear from the inner surface ofthe rotor. Nor is it practicable to true up the inner surface of therotor by machining, for this would further reduce the thickness of therotor wall with consequent further reduction in rotor strength.

The use of a conventional tubular sleeve between the rotor wall and theimpeller to take the wear is impracticable for a variety of reasons. Itwill be seen that a tubular sleeve must, of necessity, have a slidingfit with respect to the inner wall of the rotor in order to bereplaceable. This results in a clearance between the sleeve and therotor wall wherein materials subjected to separation may collect andharden, with or without corrosion of the metal, so that it becomesvirtually impossible from a practicable standpoint to remove the sleevewhen the time arrives. Moreover, difficulty is encountered in adequatelysecuring the sleeve to the rotor wall. This is because of the highresistance to relative movement between the impeller and the sleeveduring the plowing of the solids. The most feasible method for suchattachment that suggests itself is the use of a large number of screwspassing through the sleeve and entering threaded holes in the rotorwall, but the drilling of holes in the rotor wall in the case of highspeed centrifuges is impracticable in view of the resulting reduction instrength of the rotor.

I have discovered a new combination of means whereby a sleeve or liningemployed between the rotor wall and the impeller is made readilyremovable even after long periods of use and without the need of anysecuring mechanism for the sleeve. This is accomplished by employing asleeve or lining of resilient material which conforms to the innersurface of the rotor wall, and which is split or unconnected along alongitudinal line so as to be expandable under the influence ofcentrifugal force.

It is found that by making the sleeve expandable, the

EfiQfiflhZ Patented July 2, 1963 centrifugal force thereon when therotor is in motion is far more than sufficient to secure the sleeveagainst relative movement with respect to the rotor wall, even whenplowing the most diflicult of solids from the rotor.

Thus by the use of my invention, wear of the inner rotor wall isavoided, and is instead taken up by a sleeve which can be readilyreplaced with wear. Moreover, there is no need to mechanically securethe sleeve to the rotor wall.

Further features of the invention will become apparent to personsskilled in the art as the specification proceeds, and upon reference tothe drawings in which:

FIGURE 1 is an elevation partly in section of a centri fuge embodyingthe invention;

FIGURE 2 is an end view of a type of sleeve; and

FIGURE 3 is an enlarged view of the region enclosed by a dot and dashcircle in FIGURE 2.

Referring now to FIGURE 1 of the drawings, centrifuge 10 is of thescroll solids-discharge type. As shown, its rotor 11 is cylindrical inshape, and encloses an impeller member 12, which, as shown, comprises acontinuous screw 13 attached along its inner helical and spiral edge toa supporting member 14, with its outer edge partly of helical shape asillustrated at 16, and partly of spiral shape, as illustrated at 17.

, As illustrated, a pulley 29' is connected to the rotor 11, and bothrotor 11 and impeller 12 are caused to rotate,

but at a slightly different speed such as at a ditference of from 10 to60 r.p.m., by virtue of being interconnected through a planetary gearbox18, the design, construction, operation and function of which are wellknown in centrifuges of this type. A typical gear box, for instance, isshown and described in U.S. Patent 2,703,676.

As illustrated, the casing of gear box 18 is connected to rotor 11, anda driving connection between gear box 13 and member 14 is accomplishedthrough shaft 19' which extends from the interior of the gear box 18 andconnects with member 14, in a well-known manner. In couplings of thistype, it is customary to hold a sun gear (not shown) in gear box 18stationary. This is accomplished in the usual manner by mounting the sungear on a shaft 40 held stationary by mounting it in a bracket 41 andsecuring the shaft 40' by a screw 42. Any other suitable couplingbetween the rotor 11 and the impeller member 12 to effect relativerotation therebetween may be substituted, as is well understood in theart. Then too, and as is also well known, rotor 11 and member 14 may beseparately driven, but at slightly different speeds.

20 and 21' are pillow blocks containing bearings in which extensions onrotor 11 rotate. 37 and 38 are bearings between rotor 11 and member 14.39 is thrust hearing for member 14-.

The mixture of liquid and solids to be separated is fed into the rotor11 through a conduit 21, and reaches a chamber 22 inside of the member14. It then passes into the zone of centrifugation, situated between themember 14 and the inner Wall 15 of the rotor 11, through a plurality ofchannels 23 in the member 14. Due to centrifugal force generated by therapid rotation of the rotor 11 and associated parts, and the relativerotational movement of the screw 13 with respect to the rotor 11, solidsare sedimented radially outwardly of rotor 11, onto inner wall 15 whenmy invention is not employed, and are moved to the right as seen inFIGURE 1.

In the particular centrifuge shown in FIGURE 1, and when my invention isnot employed, portion 16 of screw 13 coacts with the inner wall 15 ofrotor 11 in causing movement of solids to the right, and the portion 17of screw 13 coacts with annular filler ring 30 in causing continuedmovement of such solids. Filler ring 30 is secured to rotor 11 and itsinner surface is conveniently provided with grooves extending from leftto right as q a) seen in FIGURE 1, which grooves serve to reduce orprevent any tendency of the solids flowing toward solidsdischarge ports24, to roll, grate or turn due to the relative rotation of screw 13 withrespect to rotor 11. If desired, filler ring 30 may be omitted, in whichcase its place is taken up by separated solids over which furtherseparated solids slide in moving to the right as seen in FIGURE 1.

The separated solids in completing their movement to the right as seenin FIGURE 1, are conveyed radially inwardly out of the level of theliquid in the zone of centrifugation, while continuing to be subjectedto centrifugal force to separate liquid therefrom, the liquid thusseparated flowing back to the main zone of centrifugation, and thesolids are then discharged from the rotor 11 through ports 24, each atthe time radial distance from the axis of rotation, and of which theremay be any desired number.

It will be noted that the inlets 26 of posts 24 are closer to the axisof rotation than the ports 25, which causes the separated liquid to bedischarged through ports 25 instead of through ports 24.

1 In the usual commercial embodiments of centrifuges of this type,discharge ports 25, of their equivalent, are made radially adjustable toincrease or decrease their distance from the axis of rotation, asdesired. This de creases and increases, respectively, the depth of theliquid layer in the rotor 11, but in no event is the depth of the liquidlayer increased to the point Where liquid would be discharged from therotor through the ports 24.

Solids discharged from the rotor 11 are collected in section 31 of rotorhousing 32., and are removed through hopper 33 at the bottom of section31.

Liquid discharged from the rotor 11 through the ports 25 is collected inthe section 34 of the housing 32, and is removed through the hopper 35at the bottom of section 34.

As is well known, screw 13 may be either right-hand or left-hand inshape, that is, it may advance along member 14- either clockwise orcounterclockwise, and/ or it may, through its coupling to rotor 11,rotate either faster or slower than the rotor 11. Furthermore, screw 13and rotor 11 may rotate together in either direction, that is, eitherclockwise or counterclockwise, as seen from the gear box 18. However,the shape of screw 13 and its relative rotation with respect to rotor11, by virtue of the characteristics of the coupling employed betweenscrew 13 and rotor 11, are coordinated so as to impel the separatedsolids in the zone of centrifugation to the right as seen in FIGURE 1,that is toward the discharge port 24.

Another typical and well known commercial centrifuge, otherwiseconstructed similarly to the one above particularly described, employs aconical rotor and a spiral screw conforming to the shape of the innerwall of the conical rotor with which it coacts throughout substantiallyits entire length to impel separated solids, similar to the coaction ofsection 16 of screw 13 with the inner wall of rotor 11, as previouslydescribed. A centrifuge having a conical rotor and spiral screw is shownand particularly described in the above-mentioned US. patent.

Still another typical and well known commercial centrifuge, otherwiseconstructed similarly to the one above particularly described, isprovided with a rotor having a plurality of perforations or holesthrough the rotor wall, whereby the rotor wall acts as a screen throughwhich the separated liquid escapes, in which case there is no need forports 25 for the escape of separated liquid. Such centrifuges may have aconical and/ or cylindrical rotor, but in view of the use of aperforated or screen-like wall instead of a solid wall, rotor strengthis very substantially reduced, accompanied by a substantial reduction inthe maximum permissible speed of rotation when in use.

The foregoing description of typical centrifuges is to be considered asif sleeve 45 shown in FIGURE 1 is not present, that is, as if sleeve 45were removed from FIG- URE 1, in which case portion 16 of screw 13 isconveniently of somewhat larger diameter than illustrated, so as tobring its outer edge somewhat closer to wall 15 of the rotor 11, as willbe obvious.

The construction of a typical sleeve 45 can be more clearly seen uponreference to FIGURE 2, in which it will be noted that sleeve 45 isdiscontinuous circumferentially, that is, it is provided with alongitudinal slit 46, more clearly seen in FIGURE 3. Otherwise stated,sleeve 45 is provided with longitudinal ends 47 and 48 which are joinedtogether, and which preferably are slightly spaced from each other forreasons to be hereinafter more particularly described.

The outer surface of sleeve 45 is made to conform in shape to the innersurface of the rotor, such as rotor 11 particularly described, and itsradial dimensions are preferably such that the clearance between theouter surface of sleeve 45 and the inner wall of the rotor provides asliding fit, although such precision is by no means necessary in view ofthe flexible character of the material from which sleeve 45 is made.

By providing a small space between edges 47 and 48 at slit 46, e.g. from4 to in width, and particularly between and sleeve 45 may be collapsed,by bringing edges 47 and 48 together with use of a suitable tool, tofacilitate the insertion of sleeve 45 into and its removal from theinterior of the rotor.

Sleeve 45 is preferably, though not necessarily, provided withcircumferentially spaced ribs or ridges 49, which may be secured theretoby any suitable means, such as by welding. As illustrated, ribs 49extend along the inner surface of sleeve 45 in straight lines in anaxial direction, although ribs 49 may take any other desired shape. Forinstance, in some cases it may be preferred to have ribs 4? proceedalong the inner surface of sleeve 45 generally in an opposite helicaland/ or spiral direction from that of the screw impeller, but usuallywith a substantially greater pitch, for it can be shown that, undernormal conditions of separation, the separated solids tend to progressin this manner along the inner wall of the centrifuge rotor.

Ribs 49 are particularly helpful in making separations when in theirabsence the separated solids might tend to become wedged between thescrew and the rotor wall, or otherwise tend to cause plugging.

When ribs 49 are employed, one rib 49 illustrated at 51 is preferablysecured, such as by welding, to one longitudinal edge of the sleeve,such as edge 48 in FIGURE 3, with rib 51 slidably overlapping the otheredge, such as edge 47. The result is that the slit 46 remains coveredduring operation.

As illustrated in dotted lines in FIGURE 1, one set of oppositelypositioned ribs 49 illustrated at 52 (see FIG- URE 2) are made somewhatlonger to extend beyond the edge of sleeve 45 so as to enter somewhatlarger slots 53 in annular ring 30, such arrangement serving merely as aguide for orienting sleeve 45 in rotor 11. Provision for orientingsleeve 45 is particularly helpful when the sleeve is perforated to matchthe perforations in a perforated rotor when employed.

While slit 46 has been illustrated as straight, i.e. in the form of amissing element in a surface of revolution, it is to be understood thatit may take any other suitable shape, such as curved or jagged, withoutdeparting from the spirit of the invention.

An outstanding feature of my invention is that sleeve 45 may have anydesired thickness, for the centrifugal force applied thereto, when therotor is in operation, is directly proportional to the mass of thesleeve. For practicable purposes, however, it is preferred that thethickness of sleeve 45 should not exceed A", and particularly 4'. Whiletheoretically sleeve 45 has no minimum thickness, it is preferred thatit be sufliciently thick to maintain its shape and to withstand aconsiderable degree of wear prior to the necessity for replacement.

Thus it is preferred that it be at least thick and particularly at least/32".

Sleeve 45 may be constructed of any desired substance of which metals,and particularly abrasion-resistant metals, are preferred. It is to benoted that metals generally possess the properties of flexibility andresiliency, albeit to varying degrees. Flexibility is the property ofyielding at least to a degree without breaking. Resiliency is theproperty of springing back to a former shape, which is a preferredcharacteristic facilitating the removal of sleeve 45 for replacementpurposes. It is to be understood, however, that sleeve 45 may take apermanent set while in use.

Typical metals from which sleeve 45 may be made are the various AmericanIron and Steel Institute carbon and alloy steels; ductile iron;stainless steel, such as the austenitic, martensitic, ferritic, andprecipitation hardening grades thereof; high nickel alloys, such asthose sold under the trade marks Monel, Inconel, and Hastelloy; titaniumand its alloys; copper alloys, such as aluminum bronze and siliconbronze; etc.

While extreme brittleness is generally avoided, it is to be understoodthat breaking of sleeve 45, such as along a longitudinal line oppositeslit 46, eg at 55, (see FIGURE 2), would not destroy the function ofsleeve 45, for it would still adhere to the inner wall of the rotor,being still expandable under centrifugal force, to fulfill its intendedpurpose. In fact sleeve 45 might be made in sections, such as halves,e.g. by duplicating the structure shown in FIGURE 3 at one or morepoints around the periphery of sleeve 45, in the case of halves,suitably at 55.

A typical centrifuge of the type particularly described in connectionwith the drawings has a rotor with an inner diameter of 14', and aninner axial length of 22". The axial length of sleeve 45 isapproximately for in this particular case the annular filler ring 30 hasa greater axial length than illustrated in FIGURE 1. Another typicalcentrifuge also has a rotor with an inner diameter of 14". The inneraxial length of the rotor is 30", and the axial length of sleeve 45 isapproximately 19". In each instance sleeve 45 is made of 316 stainlesssteel, including ribs 49. Both centrifuges, in view of theirunperforated rotor walls, normally operate at between 3000 and 4000 rpm.

Uses for centrifuges of the kind herein described are so widely knownthroughout industry as to require no particular description.

Having particularly described my invention, it is to be understood thatthis is by way of illustration, and that changes, omissions, additions,substitutions and/or other modifications may be made without departingfrom the spirit thereof. Accordingly it is intended that the patentshall cover, by suitable expression in the claims, the various featuresof patentable novelty that reside in the invention.

I claim:

1. The combination with a centrifuge having a rotor for the separationof solids from liquid, said rotor having zones for the discharge ofsolids and liquid, means for impelling separated solids to the zone ofdischarge of solids, said last-mentioned means comprising an impellerfor moving said solids relative to said rotor, and means for rotatingsaid rotor and for actuating said impeller, of a flexible sleeve ofthin, non-stretchable, wear-resistant material, the sleeve beingreceived into said rotor in sliding fit and being circular incross-section in contact with a corresponding area circular incross-section on the inner periphery of said rotor, the inner surface ofsaid sleeve being close to said impeller, said sleeve having a slittherein extending from one end thereof to the other so as to expandunder centrifugal force upon rotation of said rotor to grip the innerperiphery of said rotor, thereby preventing relative movement betweensaid sleeve and said rotor upon relative movement of said impeller withrespect to said sleeve in moving solids deposited by centrifugal forceon the inner surface of said sleeve toward the zone of discharge ofsolids, and a plurality of circumferentially space-d ribs secured to theinner surface of said sleeve, one of said ribs being attached to oneedge of said slit, said rib overlapping said slit in said sleeve.

2. The combination with a centrifuge having a rotor for the separationof solids from liquid with separate zones in said rotor for thedischarge of solids and liquid, said zones being axially spaced andpositioned on opposite ends of a separating zone in said rotor, meansfor impelling solids separated in said separating zone to the zone ofdischarge of solids, said last-mentioned means comprising an axiallyarranged screw for moving said solids longitudinally of said rotor, andmeans for rotating said rotor and for rotating said screw relative tosaid rotor, of a flexible and resilient sleeve of thin, Wearresistantmetal received into said rotor in sliding fit and having a smooth outersurface circular at any crosssection thereof in contact with acorrespondingly smooth area circular at any cross-section on the innerperiphery of said rotor, the inner surface of said sleeve being close tothe edge of said screw, said sleeve having a longitudinal slit thereinextending from one end thereof to the other so as to expand undercentrifugal force upon rotation of said rotor to grip the innerperiphery of said rotor, thereby preventing relative movement betweensaid sleeve and said rotor upon relative movement of said screw withrespect to said sleeve in moving solids deposited by centrifugal forceon the inner surface of said sleeve toward the zone of discharge ofsolids, and a plurality of circumferentially spaced longitudinallyextending ribs on the inner surface of said sleeve, one of said ribsbeing attached to one edge of said slit and overlapping said slit insaid sleeve.

References Cited in the file of this patent UNITED STATES PATENTS631,680 Staahlgren Aug. 22, 1899 1,064,184 Wels June 10, 1913 1,746,041Kinyon Feb. 4, 1930 2,272,675 Knudsen Feb. 10, 1942 2,283,424 Colwell etal. May 19, 1942 2,313,260 Persoons et al Mar. 9, 1943 2,495,817 Olsenet a1 Jan. 31, 1950 2,600,372 Milliken et al June 10, 1952 2,909,335Janelid n Oct. 20, 1959

1. THE COMBINATION WITH A CENTRIGUE HAVING A ROTOR FOR THE SEPARATION OFSOLIDS FROM LIQUID, SAID ROTOR HAVING ZONES FOR THE DISCHARGE OF SOLIDSAND LIQUID, MEANS FOR IMPELLING SEPARATED SOLIDS TO THE ZONE OFDISCHARGE OF SOLIDS, SAID LAST-MENTIONED MEANS COMPRISING AN IMPELLERFOR MOVING SAID SOLIDS RELATIVE TO SAID ROTOR, AND MEANS FOR ROTATINGSAID ROTOR AND FOR ACTUATING SAID IMPELLER, OF A FLEXIBLE SLEEVE OFTHIN, NON-STRETCHABLE, WEAR-RESISTANT MATERIAL, THE SLEEVE BEINGRECEIVED INTO SAID ROTOR IN SLIDING FIT AND BEING CIRCULAR INCROSS-SECTION IN CONTACT WITH A CORRESPONDING AREA CIRCULAR INCROSS-SECTION ON THE INNER PERIPHERY OF SAID ROTOR, THE INNER SURFACE OFSAID SLEEVE BEING CLOSE TO SAID IMPELLER, SAID SLEEVE HAVING A SLITTHEREIN EXTENDING FROM ONE END THEREOF TO THE OTHER SO AS TO EXPANDUNDER CENTRIFUGAL FORCE UPON ROTATION OF SAID ROTOR TO GRIP THE INNERPERIPHERY OF SAID ROTOR, THEREBY PREVENTING RELATIVE MOVEMENT BETWEENSAID SLEEVE AND SAID ROTOR UPON RELATIVE MOVEMENT OF SAID IMPELLER WITHRESPECT TO SAID SLEEVE IN MOVING SOLIDS DEPOSITED BY CENTRIFUGAL FORCEON THE INNER SURFACE OF SAID SLEEVE TOWARD THE ZONE OF DISCHARGE OFSOLIDS, AND A PLURALITY OF CIRCUMFERENTIALLY SPACED RIBS SECURED TO THEINNER SURFACE OF SAD SLEEVE, ONE OF SAID RIBS BEING ATTACHED TO ONE EDGEOF SAID SLIT, SAID RIB OVERLAPPING SAID SLIT IN SAID SLEEVE.